VPS Setup Record - SSH Security

The VPS info I have is listed in VPS Setup Record - Basics, and I have talked about how to install LAMP at VPS Setup Record - LAMP. This is a follow-up post that targets at making our VPS more secure. Remember, to use vim to edit files, you need to press i to start inserting. When you finish, type on your keyboard :wq to save and exit.

Using Strong Password

The first thing is to make the password stronger and harder to be hacked. A good password should include at least one capital letter, one number, and one symbol. It should be of length > 8, and it should NOT contain any commonly used password like what has been listed here.

Use a password manager if you are afraid of forgetting the passwords. Get a trustable password manager as listed here. Continue reading VPS Setup Record - SSH Security

Google Drive Suggestions

Strongly suggest Google Drive to include the following functionalities:

  1. The ability to sync subfolders rather than the main folder
    This has been discussed widely on the web. One workaround is to leverage Google Drive's multiple folder feature, but that is very inconvenient and can get messy easily.
  2. The ability to recovery files in a batch
    If multiple files were removed by Google Driver's bug for example (yes, I have been through that pain in a**), there is no other way but right clicking files one by one to recovery the files. There should exist a recovery function that says "recovery the files being removed xxx minutes ago."
  3. Fix the bugs in Google Drive
    There are two major bugs that exist in today's Google Drive product. One is the uplink. The transmission is based on UDP and there's not much guarantee that packets are delivered correctly (well, there is a "guarantee" but a very loose one). The large file transmission can go wrong, causing a packet sending storm that our router thinks as an attack. The Internet would be totally shut down for protection in this case. But guess what, it's just Google Drive goes wrong.
    Another is a bug that deletes the files "randomly." If there is a sync error and it is not resolved before I restart the computer, there is a chance that Google Drive thinks I personally and manually removed the un-synced folder. In this case, the folder is then marked as "deleted" and the Google Drive app tells the server to remove that folder online! WTH!

In fact if anyone searches online, there are many complaints about the issues I've mentioned above. It's been years and Google Drive isn't any better. I'm guessing this is because Google is such a big company and Google Drive team doesn't quite care about users due to the large base number of existed users.

Brief on Synthetic Aperture Radar Imaging Resolution

I assume readers already know the definitions of:

  • Frequency of a wave \(f\): number of periods per unit time
  • Wavelength \(\lambda\): distance between each period
  • Propagation velocity \(v=\frac{1}{\sqrt{\mu\epsilon}}\): wave traveling speed, here assuming the speed of light \(c=\lambda f\) in the air
  • Beam width \(\theta\): the angular spread of the radar beam, approximated by \(\theta=\frac{\lambda}{L}\) in radian, where \(L\) is the size of real aperture

Continue reading Brief on Synthetic Aperture Radar Imaging Resolution

UnwiredLab and The Fun

Never thought crawling data from a company will be found out so fast.


The thing is UnwiredLab has extensive dataset that allows them to derive the cell tower location. And they sell the number of queries for the service. Similar services include Google Map, OpencellID, Combain, CellIDFinder, etc. UnwiredLab provides a trial/free account that allows 50 queries per day, 1500 per month. Because of my research purpose, I need extensive number of queries. I wrote my crawler and wanted to test its robustness, but obviously 50 isn't enough for testing. So I created 6 accounts in a row, with Tor, trying to escape from their spam detection system.  Continue reading UnwiredLab and The Fun

Install Scapy for Mac OS Yosemite

It's not painful but it still requires a few steps. Here I log them.

First thing is to make sure you installed Python 2.x. Not sure about whether Python 3 has similar steps. Also, here I assume Homebrew is installed too. If any of the following codes result in a Permission denied error, append sudo in front the commands. Continue reading Install Scapy for Mac OS Yosemite